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The International Court of Justice’s  Advisory Opinion on Climate Change: A  New Era of Legal Accountability for States

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Authored By: Mohaman Ahmad

BPP

The accelerating challenge of climate change, with its far-reaching environmental, economic,  and social consequences, has tested the resilience of the international legal framework. For  decades, the global response has largely been anchored in diplomatic agreements,  characterized by voluntary commitments and political declarations. However, a landmark  development in international law has signaled a fundamental shift. On 23 July 2025, the  International Court of Justice (ICJ), the principal judicial organ of the United Nations,  delivered its long-anticipated advisory opinion on the Obligations of States in respect of  Climate Change. This opinion is not a mere symbolic gesture; rather, it is a historic legal  statement that fundamentally redefines the relationship between states and the global climate  system. It elevates climate obligations from discretionary political pledges to legally  enforceable duties under a comprehensive body of international law.

The ICJ’s findings are grounded in binding international law and hold significant weight,  even though advisory opinions are not legally binding in the same way as contentious case  judgments. The opinion is considered an authoritative statement regarding the state of  international law, with the power to clarify and confirm existing legal obligations. It is poised  to shape the future of climate litigation by informing both domestic courts and international  political processes. The ICJ’s pronouncements are intended to ground a new legal basis for  accountability, effectively shifting the discourse from one of aspirational goodwill to one of  legal duty and potential liability.

The Genesis of a Landmark Opinion: A Grassroots Imperative

The ICJ’s advisory opinion was not initiated by a state acting alone but was the direct result  of a dedicated, grassroots campaign. In 2019, a youth-led organization known as the Pacific  Island Students Fighting Climate Change (PISFCC) began a campaign to persuade leaders of  the Pacific Islands Forum to bring the issue of climate change to the world’s highest court.  This effort culminated in a unanimous endorsement from the 18 members of the Forum,  leading to a UN General Assembly (UNGA) resolution adopted by consensus on 29 March  2023.

The resolution formally requested the ICJ to provide an opinion on two central questions that  would form the core of the Court’s analysis. First, the UNGA asked what the obligations of  states are under international law to protect the climate system and other parts of the  environment from anthropogenic greenhouse gas (GHG) emissions for both present and  future generations. Second, it inquired about the legal consequences for states that, through  their acts and omissions, have caused significant harm to the climate system, with particular  regard for states and peoples who are especially vulnerable or affected by climate change.  The global legal community’s recognition of the issue’s importance was underscored by the  unprecedented level of participation in the proceedings, with the Court receiving 91 written  statements and 107 oral statements—the highest level of participation in a proceeding in the  ICJ’s history.

III. The Core Legal Findings: Codifying State Obligations  and Responsibility

The ICJ’s advisory opinion meticulously clarified several foundational legal principles,  providing a new, legally grounded framework for climate action and accountability. A. The Customary Duty to Prevent Significant Harm

The Court’s most significant finding was its affirmation that the customary duty to prevent  significant transboundary environmental harm applies fully and comprehensively to the  global climate system. This is a crucial finding because it means the obligation to prevent  climate harm applies to all states, regardless of their participation in specific climate treaties.  The Court articulated a stringent due diligence standard as the governing metric for this duty.  This standard requires states to use all means at their disposal to avoid activities that cause  significant harm, including the adoption of regulations for “deep, rapid and sustained  reductions of GHG emissions”. The Court also explicitly stated that states cannot delay or  refrain from taking preventive action in the face of scientific uncertainty. The risk of harm is  assessed based on the foreseeability and severity of potential damage, taking into account the  cumulative effects of a state’s activities.

The ICJ’s application of a due diligence standard addresses a historical legal challenge posed  by the diffuse and cumulative nature of GHG emissions, a classic “tragedy of the commons”  problem. By shifting the legal focus from proving direct causation for a specific climate event  to evaluating a state’s ongoing conduct and its efforts to prevent harm, the Court provides a  far more robust and judicially manageable standard for future climate litigation. The Court’s  approach confirms that a state’s individual emissions, even if “environmentally insignificant  in isolation,” can give rise to a legal obligation to prevent harm. This reframing of the legal  problem provides a much more solid foundation for climate claims, as it is based on a state’s  failure to act responsibly in accordance with the best available science from bodies like the  Intergovernmental Panel on Climate Change (IPCC).

The Duty to Cooperate

The opinion reaffirmed the customary legal obligation for all states to cooperate in good faith  for the protection of the environment. The Court found that this duty reinforces the treaty based cooperation obligations already established under the Paris Agreement. While states  retain some discretion in how they regulate GHG emissions, the ICJ clarified that this  discretion is not absolute. It must be exercised in good faith and with the required level of due  diligence, and it does not exempt states from legal accountability. This finding directly  challenges the long-held notion that states’ climate efforts are purely voluntary and exempt  from scrutiny.

State Responsibility and Reparations

Perhaps most consequentially, the Court concluded that a state’s failure to uphold its climate  obligations constitutes an “internationally wrongful act,” triggering consequences under the  customary international law of State responsibility. These consequences include the duties to  cease the wrongful conduct, to guarantee non-repetition, and to provide reparations to  affected states. The opinion directly addresses the complex issue of causation, acknowledging  that climate harm results from multiple contributing states. It held that this fact does not  exempt a state from responsibility for its contribution, stating that a “sufficiently direct and  certain causal nexus” can be established.

By applying the International Law Commission’s Articles on Responsibility of States for  Internationally Wrongful Acts and recognizing the potential for monetary compensation and  other forms of restitution, the ICJ has provided a powerful legal foundation for vulnerable  nations to pursue climate justice claims. The opinion’s acknowledgment that appropriate

remedies may include monetary compensation, disaster or debt relief, and technology transfer  transforms the concept of an “ecological debt” from a moral argument into a legal one. The following table provides a concise summary of the ICJ’s core legal findings.

Legal Concept

Legal Source(s)

Court’s Finding

Duty to Prevent Harm

Customary International Law

A long-standing duty applies to  the climate system; states must  use due diligence to reduce  emissions and prevent significant harm, even if their contribution is small in isolation.

Duty to Cooperate

Customary International Law,  UN Climate Treaties

A mandatory, good-faith 

obligation exists to cooperate on  climate action, which reinforces  treaty-based duties.

State Responsibility

Customary International Law  (ILC Articles on State 

Responsibility)

A failure to uphold climate  obligations may constitute an  internationally wrongful act,  triggering a duty to cease the act  and provide reparations.

Reparations

Customary International Law

Injured states are entitled to  reparations, which can include  monetary compensation, 

technological transfer, and other  forms of restitution for climate related losses.

Sources of Law

UN Charter, UNCLOS, Human  Rights Law, Customary 

International Law

Climate obligations are derived  from a comprehensive 

framework, not limited to  specific climate treaties like the  Paris Agreement.

Redefining the Legal Framework: Beyond a Single Treaty

The ICJ’s opinion is particularly transformative for how it situates climate obligations within  the broader corpus of international law and for its interpretation of the Paris Agreement. The Rejection of Lex Specialis

The Court rejected the argument, made by some states, that climate obligations should be  limited solely to the UN climate regime (the UNFCCC and Paris Agreement) under the  principle of lex specialis, which holds that specific law prevails over general law. The Court  firmly established that a comprehensive legal framework governs climate obligations,  including the Charter of the United Nations, international human rights law—which  recognizes a human right to a “clean, healthy, and sustainable environment”—and the United  Nations Convention on the Law of the Sea (UNCLOS). This finding is critical because it  confirms that climate change is not merely an environmental or treaty-based issue but a  fundamental matter of human rights and international law, with duties extending to all states,  not just those party to specific treaties.

Impact on the Paris Agreement’s NDCs

The ICJ’s opinion has significant implications for the Paris Agreement’s central mechanism:  Nationally Determined Contributions (NDCs). The Paris Agreement’s flexible, “bottom-up”  approach, where each party determines its own NDC, was a political compromise designed to  achieve near-universal participation. This flexibility, however, led to the perception that  NDCs were merely aspirational pledges, with no real enforcement or accountability. The  ICJ’s ruling fundamentally alters this understanding. The Court held that NDCs are not  purely discretionary. Rather, states are under a legal obligation to exercise due diligence  when preparing their NDCs, ensuring that when taken together, they are capable of achieving  the Paris Agreement’s 1.5°C temperature goal. This introduces a new layer of legal  accountability and scrutiny, directly challenging the adequacy of many current NDCs, which  are widely considered to be misaligned with the 1.5°C pathway. This new reality exposes  governments to increased legal risk if they fail to regulate emissions adequately or align their  domestic policies with international standards.

The following table provides a comparative analysis of key legal concepts as they existed  before and after the ICJ’s clarification.

Legal Concept

Status under Paris 

Agreement/UNFCCC

Status as Clarified by ICJ  Advisory Opinion

The 1.5°C Goal

A shared, aspirational objective  for the global effort to combat  climate change.

A legal benchmark that States  have an obligation to work  toward through due diligence.

Nationally Determined 

Contributions (NDCs)

Voluntary, self-determined  pledges submitted by each Party;  content is at the Party’s 

discretion.

Subject to a due diligence  standard; must, when taken  together, be capable of achieving the 1.5°C temperature goal.

State Obligation

Primarily based on treaty 

obligations under a specialized  regime; often perceived as  political rather than legal.

A legal duty stemming from a  comprehensive framework of  international law, including  human rights and customary law, not just climate treaties.

Reparations

A politically sensitive topic  addressed through non-legal  mechanisms like the “loss and  damage” fund; not legally an  obligation.

A legal consequence of an  internationally wrongful act;  injured States have the legal  grounds to claim compensation  and other forms of restitution.

Sources of Law

Primarily the UNFCCC, Kyoto  Protocol, and Paris Agreement  (lex specialis).

A holistic framework including  climate treaties, the UN Charter,  UNCLOS, and human rights law, with obligations existing 

independently of treaty 

membership.

Critiques and The Politics of Judicial Restraint While the ICJ’s opinion has been widely hailed as a major victory for climate-vulnerable nations, a comprehensive analysis must also consider its limitations. The primary critique is that, as an advisory opinion, it is not legally binding and lacks a direct enforcement  mechanism. Some commentators have argued that it may fail to compel action from  governments that lack the political will or resources to act.

The Court’s measured approach and its refusal to engage in specific “finger-pointing” at  high-emitting states have also been noted. The opinion outlines legal principles in broad and

abstract terms, offering only limited application to specific factual issues. This is not a  weakness, however, but a deliberate strategic choice to ensure institutional legitimacy and  authority. The ICJ delivered a detailed account of state obligations in a way that minimizes  direct provocation or backlash, thereby avoiding the judicial overreach that has been  criticized in other courts’ climate rulings. The fact that the opinion was unanimous—a rare  occurrence for the Court—suggests a concerted effort to project a unified and authoritative  legal front. By delivering a generalist ruling without naming specific culprits, the Court has  provided a powerful legal argument to vulnerable states while simultaneously minimizing the  diplomatic backlash from major powers. This decision serves to bolster the Court’s credibility  in the face of global scrutiny and ongoing political friction, such as that surrounding the  Court’s Vice-President on a separate, politically charged case. It is a brilliant example of the  politics of judicial restraint, a choice that shifts the terrain of the climate debate without  triggering an immediate crisis of authority.

It is also noteworthy that the ICJ’s opinion views nature as an entity external to human life,  one that impacts and is impacted by human behavior. This stands in contrast to the Inter American Court of Human Rights, which has adopted a more progressive legal framework  that views nature as a rights-holder in its own right, to be protected not merely for its effect  on human rights but because of its vital interdependence with all life on the planet. This  comparison reveals the nuanced and evolving nature of international jurisprudence on  environmental matters.

Conclusion: A New Era of Climate Accountability The ICJ’s advisory opinion represents a fundamental turning point in international climate law. It synthesizes existing legal principles to confirm that states’ obligations to address climate change are not aspirational or voluntary but are legally enforceable duties. The  opinion codifies the duties to prevent harm and to cooperate, affirms the applicability of state  responsibility to climate-related damages, and clarifies that these obligations arise from a  comprehensive legal framework beyond the confines of the Paris Agreement. The ruling  gives new legal substance to the Paris Agreement’s mechanisms, holding that NDCs must be  pursued with due diligence and in alignment with the 1.5°C goal.

While the opinion does not have a direct enforcement mechanism, its legal and moral  authority provides a powerful toolkit for vulnerable states and civil society to press for  greater accountability and action. It lays the legal groundwork for future claims for  reparations and compensation based on legal duty rather than political discretion. The  opinion’s significance lies in its capacity to spark a chain reaction that accelerates climate  litigation on a global scale and to elevate the concept of an “ecological debt” from a moral  plea to a legally defensible claim. The ICJ has made a powerful statement that the  international legal system has a crucial and growing role to play in addressing what it has  now recognized as an “existential threat”.

The Global-Local Dynamic in Climate Accountability

The ICJ’s opinion is a powerful example of how international law is grappling with the  complexities of state responsibility in a globalized, interconnected, and shared ecological  system. The collective action problem, where a state’s individual emissions might seem  insignificant but have a large cumulative effect, is now addressed through a clarified legal  doctrine. The Court also confirmed that these new legal obligations can extend to private  actors, such as corporations, that are subject to a state’s jurisdiction. While the opinion is  abstract in its pronouncements and does not “finger-point” at specific states, its findings  ground the climate debate in a shared legal reality. It provides a blueprint for what a  responsible state must do, leaving little room for inaction.

In conclusion, the ICJ’s advisory opinion marks a pivotal moment in international  environmental law. It confirms that the legal principles for climate action already exist across  a wide range of legal sources and that their collective application creates binding obligations  on all states. The opinion’s significance lies not in its binding force but in its moral and legal  authority, which empowers vulnerable nations and civil society to challenge political inaction  and press for meaningful accountability. The opinion signals that climate obligations are no  longer merely a matter of political preference but a fundamental legal duty, and it sets the  stage for a new era of global climate governance where legal, financial, and diplomatic  consequences may arise from a state’s failure to act.

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